Go Kart Tank - Build Thread

My brother and I been wanting to build a tank for some amount of time now. Our friend, he also plays paintball with us, has donated his go kart to our first tank. Down the road we want to build one from a golf cart, but our budget doesn't permit that right now.

We're planning on building a box around the engine to sit on and protect it. Then building up around the top. And covering it all in netting.

Day 1:

It doesn't even have a chain. My brother and friend broke it last fall riding it around. But, otherwise the engine runs fine and it rolls well and everything.

The big headaches I've seen and read about with these is ground clearance and weight issues. Walking the field thoroughly prior to a game and good planning/mapping of the field can counter the ground clearance issues. Going with mostly netting will be a good step to counter the weight issue. If you do have to add more exterior hard surface for some games, fiberglass isn't all that hard to do although it can be expensive.

I don't see a reverse gear on that kart. Figure out a way to back it up if you need to otherwise ground clearance might not be your only issue. If you keep it light, you could find a way to put it in neutral and back it up Flintstones style (with your feet)...but seriously...that could be an option.

The big headaches I've seen and read about with these is ground clearance and weight issues. Walking the field thoroughly prior to a game and good planning/mapping of the field can counter the ground clearance issues. Going with mostly netting will be a good step to counter the weight issue. If you do have to add more exterior hard surface for some games, fiberglass isn't all that hard to do although it can be expensive.

Good luck.

We are very familiar with the field. As long as it doesn't down pour the day before or day of it'll be fine. With the air intake/box on the top of the engine, even crossing the stream won't be a problem.

Other than a plywood box around the engine, it's gonna be all netting.

Quote:

Originally Posted by DuckTape Dude

I don't see a reverse gear on that kart. Figure out a way to back it up if you need to otherwise ground clearance might not be your only issue. If you keep it light, you could find a way to put it in neutral and back it up Flintstones style (with your feet)...but seriously...that could be an option.

Nope, no reverse. It weighs like 150lbs, if that, with all the plywood were gonna have on it. Its easy to go flintstone style with just one foot.

Tomorrow we should get everything done, except the netting and whatever we're gonna do to hold our air tank and pods in place

A few years back I built a small tank made from a used go cart very similiar to this one but of a little higher quality. Basically I covered the whole thing in pet screen. Then wrapped it in burlap camo and put a few port and view openings to stick out the markers. There is no need to put a box over the engine if you cover the whole go cart. Just make sure you leave the back of the tank clear of the burlap because of the heat of the exhaust. In the tank world we dont take many shots in the rear so heavy covering in that area isnt necessary. Just make sure you have a second inner screening between the seating and engine compartments. This way if a paintball doesnt get into the rear of the tank your protected. If you are on a low budget as you indicated this is probably one of the best ways to get started and to get into a game. Using a go cart and with your limitations as mentioned in the other posts you will be limited for best play of a go cart tank on flat or small rolling fields. Plus areas where you have a good turn radius. I dont recommend you take this go cart tank into the bush which will show your many weaknesses as mentioned. They dont manuever that well in the bush. If you stick to trails and open areas you will have better results and less complaining about being in the tank. Our go cart tank never really ever panned out to be used in combat. We used it to run recon missions on the field and players here and there. I eventually removed the screening and other materials and sold the go cart to someone. Used that money to help build my next tank. So good luck with whatever you do to it. You will find out quickly what you can and cannot do with a go cart tank of this small size.

I'm his brother, and we decided to basically have a PVC pipe frame built around the gunner. Then put a piece of wood on top of the engine to sit on so just our upper body sticks out of the top. Everything will then be covered in netting and there will be spots to stick to gun out of and shoot. We are also going to strap a pod pack somewhere inside for extra ammo and run a remote line so the gun (Etek 3 with Pinokio+nose cone) is easier to maneuver. We will also have our homemade nerf rocket launcher inside as well. Tomorrow we are supposed to get our chain and all our supplies. Hopefully it comes together as planned.

If your wanting to do a body, one thing our field owner did was used lexan. They had a big stack of old golf cart windshield that had been replaced by a local golf course. They use to make lexan windows for the big tanks out of them. But since they got smart and started netting in the windows, they decided to make a go cart tank and use the lexan windshields and body panels. they are light weight, you can paint them, cut a whole and net it in for windows, and are darn near prefect size to use on a go cart tank.

if you dont want a body, then never mind. Nothing wrong with netting. Its easy to do and works fine. And you have good visibility over a body.

We got the frame done. It went together surprisingly better than we thought it would. The only thing left to do is add all the netting. We will probably do that next week. Also, our chain came today, but it was the wrong size. We ordered the correct chain and that should come Monday. We also have to finish our nerf launcher. As you can see in the picture, this go kart is quite small. It barely fits 2 teenagers, so I couldn't image how an adult would fit inside, so this is a temporary tank. Overall, it works great as our first tank. We will try and get the netting on in the next week and post pictures ASAP. We will also have a flag pole on the side of it when we are all done.

I strongly suggest that you reinforce the frame. One diagonal brace each side from rear of roll cage roof to about the front edge of the seat will improve structural strength of the main chassis. Without it, you will probably fold the bottom frame way to easily. There are better ways to reinforce it, but that is probably the quickest/easiest on a tight budget.

Also, you have two other challenges that can be addressed if you find parts and a little cash. That cart is designed to go much too fast for PB fields, and trying to putter around at PB Field speeds will most likely fry the clutch fast. The other challenge has been mentioned, low ground clearance. To address the clearance issues, you could try to find some lawn tractor wheels. That makes the clutch problem even worse, though, so then there is the need to add a jack shaft or re-sprocket to reduce your speed. It takes just a little math, but adding a 2 to 1 reduction would probably be a good starting point for the stock wheel size, and 3,5 or maybe more to 1 reduction if you put big wheels on it.

If you know how fast the cart is now, you can figure your optimal reduction ratio to yield your target speed.

Say you want the cart to top out at 8 mph, for getting from parking lot to field. Max speed on most fields is nominally 5 mph, probably more like 3 or 4 if you have to have a tank walker (ref). IF the stock cart speed is 24 mph, then you would aim for a 3 to 1 reduction (24/8 =3). This would also mean that you would have 3 times as much torque for climbing hills. You trade torque for speed. I see you have some dirt bikes in the pix, so you probably already have a good understanding about torque verses speed. You need to use the first couple gears to launch, and shift up for top speed, but somewhere between for hills. A cheap go cart probably only has a centrifugal clutch and just one gear/speed, so figure out how fast you wanna go and gear it accordingly.

I could see how you might think this kart goes fast, but it is actually very slow. I will be surprised with 2 people, a gun setup, a nerf launcher, pods, and maybe some other stuff if it would even go 10mph, if that. So I don't how fast it will actually go. Like I said, we will get the chain soon and then we can see the speed. Hopefully it doesn't go too fast. Also, it only has a 5hp motor.

Listen guys, Build your tank the way you think it will work. You will find as you go what will and wont work. Tanking is a evolutionary process. Anyone thats been into tanking will go thru many growing pains. There is no sense giving you advice at this point because we are adults and you are teenagers.. So you wont really listen to what we have to say. You both are young so you will find out the hard way on the art of being a tanker. When you take this tank onto the field just remember. The basic standard rules is once you enter the field of play you cannot go faster then walking speed or about 5 miles an hour. This is a given rule for all tanks no matter whom they are. The other given is the Anti-Tank (AT) guys are your biggest enemy and not other tanks. You will be taken out more by them then any other means. Some missions will be short and sometimes long. But its all part of the game and the attitude you bring to it. Have fun and be safe and dont drive the tank like its still a go cart. Thats how accidents happen!

Alright. We got the chain on and it is running great. But, it does go a little too fast for the field. Hopefully once everything is done it won't go as fast. Also, another problem are hills. The tires on this thing suck and have absolutely no traction. So if the grass is wet or we have to go up a steep hill, this kart isn't doing it. The ground clearance isn't bad though. Now everything is ready for the netting.

I really would like to thank everyone for all the advice. If I didn't have to watch my bank account, I'd love to make all the changes everyone is suggesting. There's just more important things than dumping money into a paintball tank. If our parents weren't paying for the field fee and the first 3 cases of paint we'd be SOL, that alone is over $300.

But new tires will definitely be in store before the 2nd game. They're pretty much bald right now. Luckily most of the field where tanks can go is dirt/gravel. As long as it isn't muddy, we'll be in good shape.

We'll probably also get a bigger drive sprocket. I think it's only a 10 or 11 tooth right now, and it appears 14T is the biggest common size. For $10-$15, that should be the most cost effective solution to giving more torque and less speed.

I think you might be looking at the wrong sprocket, 11 or 12 teeth sounds like the sprocket on the motor. If you make your motor's sprocket larger that will make it faster and have less torque. The sprocket on the axle is the one to change to a larger size. It is probably something like 32 to 60 tooth now. If you are going to change the small sprocket, then make it smaller, though I don't know how much smaller you can go.

I might be wrong, but I thought the steeper the gearing the higher the speed and lower the torque. Therefore putting a bigger sprock on the drive shaft would make it less steep, giving more torque.

The sprocket on the motor is a 10T. Going to 14T would make quite a difference from experience I have with gearing.

CNCRouterman's right, think of it this way...if you leave the sprocket on the drive shaft alone, it takes some number of revolutions of the drive shaft to turn the axle once. If you increase the sprocket on the axel it will take more revolutions to turn the axel (the axel will turn slower). The larger sprocket also acts as a longer lever to turn the axel (increased torque).

Remember that you trade torque for speed. That part is a direct relationship. Double the speed, halve the torque. (Ok, technically, I think that is called an "inverse" relationship)

We might be getting crossed up on the terminology of the "drive" vs "driven" side of the conversation.

Not seeing clearly how your motor's drive path is set up, I will use the simplest example I know of for go carts. One chain, one centrifugal clutch with a sprocket on it, and one Driven sprocket located on the rear axle or one of the rear wheels.

If engine is turning at 3600 rpm, and it has a Drive sprocket of 11 teeth, and the axle has a Driven sprocket of 44 teeth, then you have a Reduction ratio of 4 to 1. It takes 4 full revolutions of the Drive sprocket to cause the Driven (axle) to rotate 1 full revolution. A 5 hp motor has about 6 to 8 ft lbs of torque, depending on RPM, for this discussion, I'll use the theoretical torque value at 3600 rpm, which is 7.294, round it off to 7 ft-lbs at 3600 rpm.
So, to figure Axle (wheel) rpm, you take engine rpm divided by reduction ratio, so 3600 / 4 = 900 rpm.
Torque will be the inverse of rpm. To calculate torque you multiply the engine torque by the reduction rato, so 7 x 4 = 28 ft-lbs.

Now, you have to consider how wide an RPM range is your vehicle drivable. Small engines like lawnmower and gocart engines typically have a top rpm between 3600 and 5000 unmodified. Max torque is usually around 75% of max rated RPM. Sometimes these motors are pretty close to "constant power" for that top 25% of the rpm range, which means that they actually have higher torque at 75% rpm than at 100% rpm. I am not sure what the power curve looks like for you motor, but if equipped with a centrifugal clutch, there is a minimum RPM at which you can operate, drop below than and the clutch slips or disengages. You want to be sure that you have the clutch FULLY engaged at whatever you figure is going to be your minimum speed, maybe something like 2 mph, 'cause those clutches are not all that cheap.

So, you mention 11 tooth as one of the existing sprockets. Is that sprocket on the motor? What size is the other sprocket? I assume it is bigger, and is on the wheel or axle.
Maybe post a picture?

For reference, the math formula for horse power, torque and rpm is:
T=(5252 x HP)/RPM
Where Torque is in Foot Pounds, HP is imperial horsepower (ie: 745.7 watts), and RPM is revolutions per minute.
You can re-arrange the arguments to suite what you need to find, so the following are also valid.
RPM=(5252 x HP)/T
HP=(T x RPM) / 5252